Generally, a tractor is an engineering vehicle designed to deliver a high tractive force and conduct different kinds of work in the fields of agriculture or construction. At present, tractors used in agriculture typically include a front loader provided on a front end of a tractor body, and an attachment mounted to the front loader so as to conduct various kinds of work, such as transportation, unloading, loading, etc. Furthermore, a rotavator or the like is mounted to a rear end of the tractor body by a rear link so that work such as plowing can be conducted.
In such tractors used in agriculture, power generated from an engine is classified into movement-related power which is transmitted to wheels through a transmission to enable a tractor to move, and PTO (power take-off)-related power which is used to drive different kinds of operating implements mounted to the tractor. To embody transmission of the movement-related power, a four-wheel drive system is typically used.
Typically, the conventional tractor is configured such that when a driver rotates a steering wheel in a clockwise or counterclockwise direction, the front wheels are turned to the left or the right by a steering device. In the case where the front wheel axles are directly coupled to the respective front wheels, when the steering wheel is completely rotated, angles to which the front wheels can be turned cannot be over 60°. Therefore, although the steering wheel is completely rotated, the minimum turning radius of the tractor is comparatively wide. Thus, when the tractor is required to be turned around, the tractor must repeatedly move forwards and backwards to accomplish such a task.
In the case of typical use, the tractor having the above-mentioned construction must run or turn in place depending on conditions of a work site or the kind of work. As stated above, if the minimum turning radius of the tractor is comparatively wide, the tractor cannot cope with a small area or the case where it must turn around in place, thus reducing work efficiency.